The best way to propagate clematis is by rooting cuttings. With the right combination of heat, humidity, and soil structure, the cuttings produce new roots and grow into a clone of the parent plant. Clematis can also be propagated from seeds, if grown during springtime, in a greenhouse. Hybrid clematis should always be propagated from cuttings, as seeds from hybrid varieties do not produce true to type.
Clematis can be propagated from softwood or semi-hardwood cuttings. Softwood cuttings are taken early in spring, during the first flush of growth when the wood is still green and springy. Semi-hardwood cuttings are taken in late spring or summer. These cuttings are partly mature and beginning to turn from green to brown. Softwood cuttings taken early in the season can usually be re-planted outdoors in late summer, while semi-hardwood cuttings are generally kept in a greenhouse and planted out the following spring.
Cuttings should be 4 to 6 inches (about 10 to 15 cm) long. The bottom cut should be made at a 45° angle and the top cut should be horizontal. This helps determine the top and bottom of each cutting at rooting time. All but the top set of leaves should be clipped or pinched off the clematis cutting.
To propagate clematis successfully and reliably, it is best to use a rooting hormone. Nurseries and garden centers sell powder and liquid formulas. The bottom inch (about 2.5 cm) of the cutting is dipped or rolled in the rooting hormone to stimulate root formation.
A soil-less potting mix designed for rooting cuttings can be used to propagate clematis. As an alternative, a homemade rooting mix can be made using a combination of sand, peat moss, and perlite. This creates a sterile media that retains moisture and provides sufficient drainage. A 4 to 6-inch (about 10 to 15 cm) pot works well for rooting cuttings. The pot should have one or more holes in the bottom for drainage.
The bottom third of the clematis cutting should be inserted into the rooting media, leaving the leaves exposed. A humid greenhouse is ideal to propagate clematis from cuttings. As an alternative, covering the cutting with a clear plastic bag creates a mini greenhouse. The leaves and soil should be kept damp with frequent light watering. Clematis cuttings root in approximately five weeks.
The best time to propagate clematis from seed is in late winter or early spring, in a greenhouse. A 3 to 4-inch (about 7 to 10 cm) pot usually provides enough room for germination and seedling development. Sterile seed-starting soil blends can be purchased at home and garden centers. The clematis seeds should be placed on top of the seed starting mix and covered with 1/4 inch (about 5 mm) of soil. Once the seedlings grow 4 to 6 inches (10 to 15 cm) tall they can be planted outdoors, in a garden or landscape.